- // If the interpolation error is larger than that of one level
- // at 8-bit precision, don't combine.
- if (sum_sq_error > 1.0f / (256.0f * 256.0f)) {
+ // If the interpolation error is larger than that of about sqrt(2) of
+ // a level at 8-bit precision, don't combine. (You'd think 1.0 was enough,
+ // but since the artifacts are not really random, they can get quite
+ // visible. On the other hand, going to 0.25f, I can see no change at
+ // all with 8-bit output, so it would not seem to be worth it.)
+ if (sum_sq_error > 0.5f / (256.0f * 256.0f)) {